1. Field of the Invention
The present invention relates generally to the construction of valves and valve actuators, and more particularly to a gate valve and actuator for use in vacuum processing equipment.
2. Description of the Background Art
Loadlocks, also referred to as airlocks, are routinely employed in a variety of circumstances where material must be moved from an area at a first pressure to a different area at a second pressure. The loadlock is a sealable chamber where the internal pressure can be adjusted to match the outside pressure found at one or more ports. Of particular interest to the present invention are loadlocks which allow transport of semiconductor wafers between a location at a first pressure, typically ambient, and processing equipment operating at very low pressures, such as plasma etchers and the like.
While the concept of a loadlock is straight forward, the design of loadlocks is complicated by a number of competing considerations. For example, the loadlock must be sturdy and able to withstand the differential pressures expected during operation. In particular, the loadlocks must be able to provide positive closure and sealing of the port between the loadlock and the processing chamber. Heretofore, such positive sealing has been accomplished by providing relatively complicated linkages within the loadlock which are able to move a gate closure member between a tightly sealed position and an open position free from obstructing the port. See, for example, U.S. Pat. No. 4,433,951 where a particular actuating linkage is illustrated in FIGS. 2A-2C.
The valve actuating mechanisms of the prior art, and of U.S. Pat. No. 4,433,951 in particular, suffered from a number of disadvantages. In the first place, the mechanisms have included a large number of exposed joints, bearings, hinges, and the like, which generate particulates whenever the mechanism is actuated. Such particulates can deposit on the wafers and interfere with the desired processing operation. Moreover, such joints are difficult to lubricate in a low pressure environment, where the lubrication fluid quickly vaporizes. In addition, location of the gate valve actuating mechanism within the loadlock increases the size of the loadlock required for a given application. Such increased size in turn, increases the time and power required to draw a vacuum, as well as increasing the capital costs associated with producing the loadlock.
For these reasons, it would be desirable to provide a gate valve assembly for use with a low pressure loadlock, where the assembly includes few or no joints, bearings, hinges and the like exposed to the low pressure environment within the loadlock. It would be particularly desirable if the gate valve assembly occupied a minimum volume within the loadlock, and provided for substantially complete retraction of the gate member away from the port so that access through the port is unobstructed.